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Back feed breaker panel or use lugs?

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MT off grid

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I am installing two growatt 3000tl lvm-es in my home, they will be wired as split phase into their own panel feeding some outlets, I have seen videos of people using a double poll breaker to back feed the panel and others use the L1 & L2 lugs in the panel, does anyone have any information on why it's done one way or the other
 
If the system isn't connected to the grid, and can not be connected to the grid accidentally, it really doesn't matter. What does matter is that you provide proper over-current protection on all circuits, including the feed lines from the inverter(s).

My off-grid system feeds my home's grid-connected breaker panel, but it does so through an interlocked double-pole breaker that can not be turned on unless the main breaker leading to the grid is turned off.

Your post is a bit confusing because you used the term "back feed the panel". Back feeding usually refers to a panel that is already connected to a power source, usually grid power, or possibly referring to a sub-panel that is powered by the home's grid connected panel.

Back feeding is a description used to indicate a second alternative power source when the primary source is unavailable.
 
MurphyGuy said:
If the system isn't connected to the grid, and can not be connected to the grid accidentally, it really doesn't matter. What does matter is that you provide proper over-current protection on all circuits, including the feed lines from the inverter(s).















My off-grid system feeds my home's grid-connected breaker panel, but it does so through an interlocked double-pole breaker that can not be turned on unless the main breaker leading to the grid is turned off.















Your post is a bit confusing because you used the term "back feed the panel". Back feeding usually refers to a panel that is already connected to a power source, usually grid power, or possibly referring to a sub-panel that is powered by the home's grid connected panel.















Back feeding is a description used to indicate a second alternative power source when the primary source is unavailThank you fo4 your replyable.







If the system isn't connected to the grid, and can not be connected to the grid accidentally, it really doesn't matter. What does matter is that you provide proper over-current protection on all circuits, including the feed lines from the inverter(s).







My off-grid system feeds my home's grid-connected breaker panel, but it does so through an interlocked double-pole breaker that can not be turned on unless the main breaker leading to the grid is turned off.







Your post is a bit confusing because you used the term "back feed the panel". Back feeding usually refers to a panel that is already connected to a power source, usually grid power, or possibly referring to a sub-panel that is powered by the home's grid connected panel.







Back feeding is a description used to indicate a
Click to expand...

Thank you for the reply, i guess I have always been told that anything other then using the lugs is called back feeding, I only have a small 6 slot panel so using a double poll to feed the panel uses a lot of my space, I would rather just feed the panel through the lugs, I'm guessing that as long as I have go connection ti the grid in any way I could just use the lugs, I have an interlock and manual transfer switch from another project that I plan to use when I connect it to my house but for now i just want it to stay off grid and feed outlets
MurphyGuy said:
second alternative power source when the primary source is unavailable.
Click to expand...
 
MT off grid said:
Thank you for the reply, i guess I have always been told that anything other then using the lugs is called back feeding, I only have a small 6 slot panel so using a double poll to feed the panel uses a lot of my space, I would rather just feed the panel through the lugs, I'm guessing that as long as I have go connection ti the grid in any way I could just use the lugs, I have an interlock and manual transfer switch from another project that I plan to use when I connect it to my house but for now i just want it to stay off grid and feed outlets

Just for clarification, are you saying that everything should be protected including the iverter feed Going into the panel even for off grid applications?
Click to expand...
 
Just for clarification, are you saying that everything should be protected including the iverter feed Going into the panel even for off grid applications?

Yes. It doesn't matter if you're grid tied, off grid, or wiring up extra lights on your 12volt car, atv, snowmobile, or dirt bike. Every wire in an electrical system needs to be protected by an over-current device (circuit breaker, fuse, etc) to prevent excess current from causing the insulation to melt and catch fire.
Yes, even a 12 volt light on your motorcycle should have an inline fuse or something.

Just ask yourself this when wiring things.. 1) How much current is this wire rated for and 2) What will prevent this wire from exceeding that specification?

A common misconception about fuses and circuit breakers is that they are there to protect your devices like your television, computer, stove or microwave. They are not. Over current protection devices are there to protect the wires, not the devices connected to the wires.
 
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I understand the reason for fuses etc but on an off grid system wouldn't the 15 amp breakers protect the wires going to the inverter? Seems like feeding two inverters through a double poll breaker to then feed 15 amp breakers os doubling up on breakers, if an appliance failed on a 15 amp circuit wouldn't in turn protect everything upstream from there.
 
MurphyGuy said:
My off-grid system feeds my home's grid-connected breaker panel, but it does so through an interlocked double-pole breaker that can not be turned on unless the main breaker leading to the grid is turned off.
Click to expand...
I also use a set of interlocked breakers so that if I have to take the hybrid off line for maintenance and/or a firmware upgrade, I can power the critical loads panel from the grid.
 
MT off grid said:
wouldn't the 15 amp breakers protect the wires going to the inverter? Seems like feeding two inverters through a double poll breaker to then feed 15 amp breakers os doubling up on breakers, if an appliance failed on a 15 amp circuit wouldn't in turn protect everything upstream from there.
Click to expand...
As @MurphyGuy mentioned earlier the over current devices are to protect the wires. This includes the wire from the inverter to the breaker panel. Most inverters contain a circuit breaker so if your's has one your wires are protected by that breaker. The redundant breaker at the service panel is part of the interlocked system. if you choose to do that.
 
Ampster said:
As @MurphyGuy mentioned earlier the over current devices are to protect the wires. This includes the wire from the inverter to the breaker panel. Most inverters contain a circuit breaker so if your's has one your wires are protected by that breaker. The redundant breaker at the service panel is part of the interlocked system. if you choose to do that.
Click to expand...
 
Growatt already hadls a 40 amp breaker built in but I see some videos feeding a double poll and other feeding the lugs, I guess feeding a breaker is just extra safety measure
 
If these are the only wires that will ever feed the panel. Then going to the main lugs is fine. Overcurrent protection should be located at the source end of conductors. In this case, the inverter end. If the wires are sized correctly, the inverter output protection also protects the wiring.
And feeding the bus bars in a panel from one of the output locations (not main lugs or main breaker) is considered backfeeding the bus.
 
MT off grid said:
I understand the reason for fuses etc but on an off grid system wouldn't the 15 amp breakers protect the wires going to the inverter? Seems like feeding two inverters through a double poll breaker to then feed 15 amp breakers os doubling up on breakers, if an appliance failed on a 15 amp circuit wouldn't in turn protect everything upstream from there.
Click to expand...
How many 15 amp breakers? (rhetorical question). Each 15 amp breaker can have up to a 15 amp load on it.. If you have 10 amps load A, 12 amps on load B, and 8 amps on load C, then 10+12+8 = 30 amps. So your panel is pulling 30 amps from your inverter and none of your 15 amp breakers are going to trip.

If your growatt already has a 40 amp breaker, then we could consider two options based upon that.
1) You can depend on that 40 amp Chinese breaker and make sure the wires you install between that inverter and your panel are capable of handling the full 40 amps.

Or

2) (most recommended) Install an 8 gauge wire (preferably a 6 ga wire) and put a 40 amp breaker in your panel to make sure the Chinese breaker doesn't behave like most other Chinese products.

Seriously, I'd go with option 2 and a 6ga wire. And don't forget to liberally apply NOALOX paste to any cheap aluminum cable terminal blocks. And if you don't do this stuff often, use an actual torque wrench to make sure you tighten the screws down properly. Too much or too little is bad.
 
MurphyGuy said:
How many 15 amp breakers? (rhetorical question). Each 15 amp breaker can have up to a 15 amp load on it.. If you have 10 amps load A, 12 amps on load B, and 8 amps on load C, then 10+12+8 = 30 amps. So your panel is pulling 30 amps from your inverter and none of your 15 amp breakers are going to trip.



If your growatt already has a 40 amp breaker, then we could consider two options based upon that.

1) You can depend on that 40 amp Chinese breaker and make sure the wires you install between that inverter and your panel are capable of handling the full 40 amps.



Or



2) (most recommended) Install an 8 gauge wire (preferably a 6 ga wire) and put a 40 amp breaker in your panel to make sure the Chinese breaker doesn't behave like most other Chinese products.



Seriously, I'd go with option 2 and a 6ga wire. And don't forget to liberally apply NOALOX paste to any cheap aluminum cable terminal blocks. And if you don't do this stuff often, use an actual torque wrench to make sure you tighten the screws down properly. Too much or too little is bad.
Click to expand...
 
I have decided to go with feeding a 50 amp double poll breaker and avoiding the lugs all together, I'm not a fan of the cheap push button breakers in the growatt , i really appreciate your help and very detailed explanations
 
MT off grid said:
I have decided to go with feeding a 50 amp double poll breaker and avoiding the lugs all together, I'm not a fan of the cheap push button breakers in the growatt , i really appreciate your help and very detailed explanations
Click to expand...
50 amp breaker with what size wire?
 
8awg, running two inverters in split phase so each inverter will be on 25 amp breaker, 3000÷120=25, am I correct or should I have gone 3000÷120×1.25=31.25 and gone with a 60 amp double poll
 
MT off grid said:
8awg, running two inverters in split phase so each inverter will be on 25 amp breaker, 3000÷120=25, am I correct or should I have gone 3000÷120×1.25=31.25 and gone with a 60 amp double poll
Click to expand...
Just make sure the breaker size and wire size match. If the inverter puts out more than the breaker can handle, you'll simply be in the dark for a few seconds while you reset the breaker...

What is NOT acceptable is using a 40 amp wire on a 50 amp breaker.. but you CAN use a 50 amp wire on a 40 amp breaker, that's perfectly fine.
 
MurphyGuy said:
Just make sure the breaker size and wire size match. If the inverter puts out more than the breaker can handle, you'll simply be in the dark for a few seconds while you reset the breaker...



What is NOT acceptable is using a 40 amp wire on a 50 amp breaker.. but you CAN use a 50 amp wire on a 40 amp breaker, that's perfectly fine.
Click to expand...
 
Everything I have read says 8 AWG THHN is good for 55 amps, electrician I talked to said he rates it more in the 40 amp rating, the growatt manual says 8AWG so I figured it should be good to go on a 25 amp breaker
 
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